1. Field of the Invention
The present invention relates to an oscillation device which causes an oscillator to self-oscillate, a scanning-type scanner device such as a laser projector or laser rangefinder that is equipped with this oscillation device, and an information terminal equipped with this oscillation device. The present invention also relates to a phase-shift amount adjustment device and a phase-shift amount adjustment method which adjust an amount of phase shift in a phase shift unit of this oscillation device.
2. Description of the Related Art
Conventional oscillation devices cause an oscillator to self-oscillate by supplying the oscillator with a drive signal at a frequency that is made to match the mechanical resonance frequency of the oscillator (for examples, see Japanese Patent Application Laid-Open Publication No. 2008-124192, Japanese Patent Application Laid-Open Publication No. 2005-351820, and Japanese Patent Application Laid-Open Publication No. 2010-066008).
The oscillation devices cause the oscillator to self-oscillate by sending a drive signal as positive feedback to the oscillator by making the amount of phase shift in a single complete loop an integer multiple of 0° or 360°. Furthermore, the oscillation devices also automatically control gain such that the amplitude of the oscillator stays constant.
The oscillation devices have the advantage of being able to produce high oscillations in the oscillator at a low drive power because the oscillator is made to resonantly oscillate.
However, variations between individual oscillators, changes in the ambient environment of the oscillation device (such as temperature changes), and the like, cause transfer characteristics to be different from design or desired values, and as a result, the amount of phase shift in a single complete loop ends up deviating from 0°.
Self-oscillation is possible even when the amount of phase shift in a single complete loop deviates somewhat from 0° (±15° or so), but the amplitude of the oscillator cannot be kept constant unless the amplitude of the drive signal is made larger than it is when there is no deviation. Thus, there are problems in that drive power is increased while drive efficiency is worsened. Moreover, if the amount of phase shift in a single complete loop deviates too much from 0°, the additional problem of being unable to initiate self-oscillation also arises.